1. Field of the Invention
The present invention relates in general to valves for mineral recovery wells, and in particular to actuators to actuate valves.
2. Brief Description of Related Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body, and moves linearly to obstruct flow through the bore or allow flow through the bore. Some gates have an aperture that aligns with the bore to allow flow. The gate can be normally open, and thus the gate is closed when it is moved linearly to push the aperture out of alignment with the bore. Alternatively, a gate can be normally closed, and thus the gate is opened when it is moved linearly to position the aperture in alignment with the bore. Regardless of whether the gate is normally open or normally closed, the gate is moved, or actuated, by a valve actuator.
An indicator stem protrudes through the cap of the housing of a typical valve actuator. The indicator stem is part of a sealing nut assembly that extends upward from the plate inside the valve actuator housing, or is threadingly connected to the top surface of the plate. The indicator stem sealing nut sealingly engages a bore of the plate. Leaks can occur between the indicator stem sealing nut and the plate. In pneumatic type actuators having a diaphragm, the sealing nut must be removed to replace the diaphragm.
In some cases, the actuator can be manually actuated by pressing against the indicator stem. The force on the stem, however, can damage the stem or internal components of the actuator. It is desirable to be able to externally actuate the valve without exerting forces on the stem that can damage the actuator. It is also desirable to be able to remove and replace the stem without breaking seals between the sealing nut arid the plate or diaphragm.